Let's not decide in the generic ci/ part how many jobs to run in
parallel; different CI configurations would favor a different number of
parallel jobs, and it is easy enough to hand that information down via
the `MAKEFLAGS` variable.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>